The present invention relates generally to friction shoes for use in railway car trucks and, more particularly, to friction shoes having a resilient, elastomeric pad on the sloped faces thereof.
Railway freight car trucks generally comprise two wheelsets mounted on axles, with both axles joined by and supporting side frame castings. The side frame castings are located outboard of the railway wheels, and are mounted on the axles by roller bearing assemblies with adapters. A bolster casting is centrally mounted parallel to the wheel axles in the side frame castings. Each end of the bolster is supported in the respective side frame casting by a spring group. Depending on the loading characteristics of the railway car, the spring group can comprise a various number of outer coils, inner coils or shock absorbing devices. Typical railway freight cars have nine spring positions.
Each side frame includes two centrally located vertical columns which extend from the bottom of the spring group support floor to the upper compression member of the side frame casting. These side frame columns form an opening for the end of the bolster.
The weight of the railway freight car is supported by the side bearings and center plate of the bolster. Two major types of car instability are directly related to the type of interconnection between the bolster end and the side frame bolster opening. These instabilities are truck hunting which usually occurs at high speeds wherein the truck turns out of square with the rails causing it to weave down the track, usually with the wheel flanges striking the rails. Further, truck lozenging can accompany such hunting wherein the bolster turns out of square with the side frames. The other type of instability is referred to as rock and roll which refers to an excessive lateral rocking of the freight cars, usually occurring at low speeds. Solutions to both types of instability include the provision of a winged friction shoe between each side frame column and the adjacent bolster side. Accordingly, each bolster end includes two friction shoe pockets, each comprising two sloped surfaces against which corresponding sloped surfaces of the friction shoe abut. The friction shoe also includes a generally flat, generally vertical face which abuts a friction wear plate welded and/or bolted to each side frame column.
The lever arm provided by the winged friction shoe acts to square the bolster with the side frame which helps to reduce the wheel/rail angle of attack on curves and accordingly, reduce the possibility of truck hunting. Further, the damping affect of the friction shoe surfaces against both the sloped surfaces of the bolster friction shoe pocket and the side frame column friction plate tend to provide a dampening force to the oscillations of the bolster in the side frame spring pocket to lessen lateral rocking of the freight car.
Due to the relatively high cost of the truck bolster, it is undesirable for the sloped surfaces of the generally harder friction shoe to wear into the bolster sloped surfaces. Excessive wear in the bolster sloped surfaces eventually requires the replacement of the bolster, as repair of such surfaces is impractical.